Photosensitive tube



Jan. 15, 1946. 1.. A. ADAlR PHOTO-SENSITIVE TUBE File d Feb. 27, 1942La/[cnce A. Ada/k" Patented Jan. 15, 1946 PHOTOSENSITIVE TUBE LallanceA. Adair, Austin, Tex., assignor to Light Control, Inc., Austin, Tex., acorporation 01" Texas Application' February 27, 1942. SerialNo. 432,550

8" Claims;

This invention relates to" new and useful .improvementsin-photo-sensitive tubes; and in particularto that 'class of tubes whichmay be designated as "photo-sensitive relaxation oscillators.

One object of this invention is to provide an improved photo-sensitivetube in which a' source oi llght is utilizedto break a series ofoscillations and thereby control or'actuate by means of relays or othersuitable equipment, certain instruments or devices which it is desiredto operate in accordance with varying light'conditions.

It is another'object of this invention to provide an improvedphoto-sensitive tube wherein light rays are directed onto aphotosensitive surface soas to cause the surface and the space betweenit and the'filament to become blanketed or clouded with photoelectronsemitted from the surface dueto the impinging of the light rays, wherebyan oscillating discharge between the surface and any other element inthe tube is preventedandcurrent ceases to flow to the tube.

Still another object or this invention is to provide an improvedphoto-sensitive tube wherein the photo-sensitive surface is separatedfrom the balance of the tube, so that photo-sensitive material maybeplaced thereupon by sputtering or in any other suitable manner, withoutdepositing a photo sensitive material upon the balance of the elementsin the tube. The separation is not primarily for control of thephoto-sensitive material as some previous similar devices have been butis putin this form so that various gas fillings, or a vacuum, may beused irrespective of the condition prevailing in the oscillating triode.This aids both in use and in'manufacture, and, further, it permits aflexibility of use with auxiliary circuits.

Still another object of the invention is to provide a photo-sensitivetube with an extremely high control ratio and at the sarne'time capableoi supplying relatively large currents at low voltages for actuation ofrelays, and which is operable'on either A. C. or D; C. current, andwhich is especially serviceable in the range below twenty volts.

Yet another object of the invention is to provide an improvedphoto-sensitive tube having means for concentrating light from anexterior A construction designed to carry out theinvention will behereinafter described, togetherwith other features of the invention.

The invention will be more readily understood from a reading of [thefollowing specification and by reference to the accompanying drawing, inwhich an example of the invention is shown, and wherein:

Figure 1 is an isometric view, partially broken away, of a tubeconstructed in accordance with this invention,

Figure 2 is a similar view of a modification of the invention, and

Figure 3 is a view of a sample wiring diagram.

In the drawing, the numeral lildesignates the gas-filled shell orenvelope of the tube, the en velope being formed of glassor some othersuitable material. Mercury vapor or any other suitable gas may beutilized to fill the tube, it being desirable to use a gas having anignition voltage characteristic within the range in which it is desiredto operate the tube. If desired, the envelope may be masked upon theinside or outside with some suitable type of opaque and/or conductingcoating (not shown), said coating, in some instances, improving certaindesirable operating characteristics of the tube.

The envelope I0 is provided with the usual base I I through which theusual connection prongs l2 extend. The tube is provided in its interiorwith a filament l3 connected by suitable leads M to a pair of the prongsI2. Also, a plate I5 is disposed in the tube in relatively closeproximity to the filament l3, and is-connected by a lead I6 .to anotherof the prongs l2. Theplate I5 is substantially disk-shaped in form andis disposedat an angle to the longitudinal axis of the tube. It is to benoted. of course, thatthe plate l5 may be of any desirable shape orsize. Asmall spot of photo-sensitive material 11 is disposed in thecenter of the plate I5. This photo-sensitive material may be of anymaterial which emits electrons under: the action of light such ascaesium or other alkaline earth material capable of producingphotoelectrons under the'influence of light.

A grid l8 is'disposed between the'filament l3 and'the plate [5, and isconnected by a lead l9 to the fourth prong l2. A convex lens 20 ismounted in the upper end of the envelope l0 so as to have its opticalaxis in alinement with the longitudinal :axisof the tube. The lens 20 isof such radius of curvature, and is so spacedfrom thephoto-sensitivespot IT, as tohave the principal focus of the lens coincidewith thelocation of the spot II. Thus, light falling upon the lens 20 isconcentrated from the entire surface of the lens into an intense spot oflight which falls upon the photo-sensitive spot H.

In operation, the filament I3 is heated through the leads I4 to atemperature sufiicient to produce an ample supply of electrons bythermal emission, and a voltage is placed between the leads I 4 and I6,and thus between the filament I3 and plate I5. The leads l4 and I6 arealso shunted exteriorly of the tube through a suitable condenser (notshown), so that an intermittent discharge or oscillating discharge takesplace between the filament and the plate, the plate of course carryingthe positive charge. The charge on the condenser builds up from thesource of voltage until the charge reaches the break-down or ignitionvoltage of the tube, at which time the condenser discharges through thegap between the filament and the plate. After the voltage has dropped tothe point of extinction of the arc between filament and plate, thisdischarge will be broken and the condenser will commence to charge againuntil an ignition voltage is reached. Thus, an oscillating discharge isinstituted within the tube.

The rapidity or frequency of this discharge is determined by theparticular design of the tube and will depend upon the volta e appliedand upon the resistance and capacitance of the various leads both withinthe tube and the asso ciated circuit and equipment (not shown). The gridI8 serves as a control, and any desirable voltage may be placedthereupon so as to increase or decrease the break-down or ignitionvoltage of the tube.

It is pointed out that the oscillating discharge takes place only whenthe tube is not exteriorly illuminated and that the light given off bythe discharge and by the filament I3 is not or" sufficient intensity asto block operation of the tube by affecting the photo-sensitive spot IT.This light is suilicient, however, to raise the point of arc extinctionalmost to the point of the breakdown voltage so that the arc isextinguished rather quickly as the voltage between the plate and thefilament begins to drop. However, as light impinges upon the tube alongits longitudinal axis, it is concentrated by the lens 20 into an intensespot upon the photo-sensitive substance IT, thereby causing saidsubstance to commence the emission of electrons.

The plate I during arcing is positive in charge and the electronsemitted are negative in charge. Thus, during the dark portion of theoscillation cycle, the electrons are not discharged by the positivecharge of the plate, but form a blanket around the plate and greatlyincrease the ignition voltage of the tube, since a much higher voltageis required to cause an are between the filament and the plate while thecloud of electrons is present. The action of these negative electrons issimilar to the action of the negative potential of the grid I8 in thatsaid electrons increase the break-down potential of the tube. Since thegrid is adjusted to such a value that the periodic break-down is barelybeing maintained, the action of light increases the break-down potentialto such a value that said periodic break-down cannot occur and thecurrent flowing to the plate I5 is small or is substantially shut off.In this manner the tube acts as an electric valve to allow current toflow while in the absence of exterior light, but to shut ofi the currentin the presence of exterior light.

It is manifest, that the lens 20, by concentrating the available lightinto an intense spot, causes the tube to be sensitive and to operate ata much lower light intensity than possible with other photo-sensitivetubes.

In Figure 2, there is shown a modification of the invention, in whichthe photo-sensitive surface is placed in a separate compartment from thebalance of the tube elements. The tube shown in Figure 2 is providedwith the usual envelope 2|, having a base 22 with prongs 23 projectingtherethrough. A plate 24, a filament 25 and a, grid 26 are mountedwithin the envelope M and connected by suitable leads to certain of theprongs 23.

The envelope 2| is formed with a stricture 21 near its upper end and asuitable insulating member 28 is positioned at the stricture 21 so as toseparate the envelope into a lower and upper compartment, the lowercompartment being occupied by the plate, filament and grid.

A second plate 29, having a spot of photo-sensitive material 30 at itscenter, is mounted in the upper compartment, and is connected to asuitable lead 3|. A ring electrode 32 is positioned above the plate 29and connected to a suitable lead 33, while a convex lens 34 is mountedor integrally molded in the upper end of the envelope 2I above the plate29 and electrode 32. The leads 3| and 33 extend downwardly through thelower compartment of the envelope, being insulated with glass tubing 35or some similar substance. and having their lower ends connected toprongs 36,which project from the lower end of the tube.

The provision of the separate upper compartment to contain thephoto-sensitive surface, allows the photo-sensitive substance to besputtered thereupon without the possibility of some of the materialdepositing upon other elements in the tube such as the plate or grid, orupon the leads thereof. Thus, when light strikes the tube only thedesired spot becomes photo-sensitive and emits electrons. If there wereany chance deposits of the photo-sensitive material upon other elementsof the tube, they might emit electrons so as to affect the sensitivityor other operating characteristics of the tube, or render the tubeinoperative. Also, the separate compartments allow the use of differentgases and/or pressures in the two chambers so that varied operatingcharacteristics may be obtained.

The operation of this modified form of the invention is substantiallythe same as that of the form shown in Figure l, with the exception thatthe electrode 32 is suitably connected to the grid 26 so as to place anegative charge upon the grid when light strikes the photo-sensitivespot 30. whereby the ignition voltage of the tube is increased over thatvoltage available between the plate 24 and the filament 25.

These tubes may be utilized in various fashions. An instance of such anuse would be to connect a relay in circuit with the plate I5 and thefilament I 3 as shown in Figure 3 of the drawing.

In Figure 3, the tube shown in Figure 1 is utilized. The leads I4 areconnected across a portion of a battery 40, while the filament I3 andthe plate I5 are connected across the entirety of the battery. Acondenser II is shunted across the leads of the filament and the plate.while the grid I8 is connected to a rheostat or variable resistance 42shunted across the leads I4. The connection between the battery and theplate I5 extends through the coil 43 of a relay M, which has the usualspring-mounted armature and a closed position, respectively. wire 48' isconnectedlito 'the.;armature' iitoi complete theicir- "rheir'elay-"flmaybe o'ithe "slow-jop'ening type provided with a shading slug(notfshown), or-acondenser-48 maybe shunted across the-coil 43, as shownin 'dottedlines, to cause the relay to remain closed an instant afterthe circuit through the coil has been broken.

In the absence of exterior light, the condenser ll charges from thebattery 40, until the breakdown voltage of the tube is reached, at whichtime the tube arcs or discharges and the voltage drops to the point ofextinction, after which the condenser ll again charges, etc. Thefilament I3 is heated from a portion of the battery so as to emitelectrons and make possible the arcing or discharge of the tube. Thusthe condenser 4| causes the tube to oscillate or operate intermittently,so that the arc may be broken when desired. Other means than thecondenser may be utilized for such purposes.

The potential of the grid may be adjusted by means of the variableresistance 42 so as to set the break-down voltage and other operatingcharacteristics of the tube.

The relay may be of any desirable type and thus may operate in manydifferent fashions. Current fiows through the coil of the relay when thetube is not exposed to exterior light. However, in the presence of lightthe current is stopped and the armature of the relay moves to an openposition, to open or close contacts as the case may be. This operationis in accordance with the description given hereinbefore.

The tube may be used in many other applications, and under many varyingconditions.

What I claim and desire to secure by Letters Patent is:

1. A light responsive system including, an envelope, a plurality ofelectrodes in the envelope, one of said electrodes having aphoto-sensitive area, a source of electrical potential connected betweenthe latter electrode and another electrode so as to cause under normalconditions a stream of electrically-charged particles to fiow betweenthe two electrodes, a condenser connected across said two electrodes forapplying the electrical potential intermittently thereto, whereby anintermittent current flows between said two electrodes, and meansembraced by said envelope for directing light upon the photo-sensitiveelectrode so as to raise the discharge potential of the system andsubstantially stop the flow of electricallycharged particles in saidsystem.

2. A light responsive system including, a gasfilled envelope, a filamentin the envelope, a circular plate disposed at an angle and bearing aphoto-sensitive area in the envelope, a grid in juxtaposition to thefilament and plate, leads from the various electrodes, a lens mounted inthe envelope so as to converge a beam of light from an exterior sourceonto the photo-sensitive area or the plate, means connected across thefilament and plate for heating the filament, means for placing apotential between the filament and the plate, means connected to thegrid for applying a variable control potential to the grid, and acondenser connected across the plate and filament leads for intermittingthe potential thereacross so as to cause an intermittent discharge ofthe system, the photo-sensitive area acting under exterior light toblock the discharge and shut off the current flowing through the system.

i3. fAilight responsivesystem including anrenvelopelihaving a pluralityoig-gas-filledseparate compartments, a iphotoesensitive plate in -onecompartment, a' ring electrode adjacent" said plate, ta. plate,a""filament and'a grid in another compartment, alloi'fthe'electrodes"having'ieads,

' af'lens suppo'rte'dlby the envelope for; concentrat- "inglight'irom anexteri'orsourcepnto thephotosensitive plate, and a condenser connectedacross the plate and ring electrode for intermitting a potential acrossthe photo-sensitive plate and the ring electrode to cause anintermittent discharge of the system, the photo-sensitive plate actingunder the influence of exterior light to raise the discharge potentialof the system above that supplied by means of the condenser and thusshut ofl the intermittent discharge of the system and thereby control adischarge between the plate and the filament in the second compartment.

4. A light responsive system including, an envelope, a plurality ofelectrodes in the envelope, one of the electrodes having photosensitivemeans associated therewith, a source of electrical potential connectedbetween two 01' said electrodes to cause under normal conditions astream of electrically-charged particles to fiow between the twoelectrodes, a condenser connected across the two electrodes for applyingthe electrical potential intermittently to the electrodes to permit anintermittent current flow therebetween, and means for directing lightupon the photo-sensitive means to raise the discharge potential of thesystem and substantially stop the fiow of said electrically-chargedparticles.

5. A light responsive system including, an envelope divided into aplurality of chambers, a plurality of electrodes in two of the chambers,photo-sensitive means within one of the chambers, a source of electricpotential connected between two of the electrodes in each chamber forcausing a flow of electrically-charged particles between said twoelectrodes, and a condenser connected across said two electrodes forapplying the electrical potential intermittently to the electrodes so asto cause an intermittent discharge of the system, the photo-sensitivemeans acting under the influence of exterior light to raise thedischarge potential of the system above that applied by the intermittentmeans and thereby shut off the intermittent discharge of said system bycontrolling the discharge between the electrodes in the other chamber.

6. A light responsive system including, an envelope, a plurality ofelectrodes in the envelope, a source of electrical potential connectedbetween two of the electrodes for causing a stream ofelectrically-charged particles to flow between said two electrodes, acondenser connected across said two electrodes for applying theelectrical potential intermittently to the electrodes so that anintermittent current flows therebeween, and photo-sensitive means withinsaid envelope and acting under the influence of exterior light to raisethe discharge potential of the system and substantially stop the flow ofelectrically-charged particles.

'7. A light responsive system including, a gas filled envelope, afilament in the envelope, a plate in said envelope, the plate having aphoto-sensitive area, a grid in juxtaposition to the filament and plate,leads from said filament, plate and grid, means connected across thefilament and plate for heating the filament, means connected across thefilament and plate for applying a potential between said filament andplate, means connected to the grid for applying a variable controlotential to the grid, and a condenser connected across the leads of theplate and filament for intermitting the potential therebetween so as tocause an intermittent discharge of the system, the photo-sensitive areaacting under the influence of exterior light to raise the dischargepotential of the system so as to block the discharge and therebysubstantially stop the current flowing through the system.

8. A light responsive system as set forth in claim 7 wherein the meansfor applying a variable control potential to the grid includes avariable resistance.

LALLANCE A. ADAIR.

